Transformer system including a large number of magnetically independent transformer elements



Nov. 4, 1969 G; l. PAPALEONIDAS N TRANSFORMER SYSTEM INCLUDING A LARGE'NUMBER 0F MAGNETICALLY INDEPENDENT TRANSFOMER ELEMENTS Filed Aug. 15, 1966 LOAD PIC-3.!

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United States Patent 3,477,016 TRANSFORMER SYSTEM INCLUDING A LARGE NUMBER OF MAGNETICALLY INDEPENDENT TRANSFORMER ELEMENTS George Ioannon Papaleonidas, 2 Patriarchou Grigoriou, Aegeleo-Athens, Attica, Greece Filed Aug. 15, 1966, Ser. No. 572,355 Int. Cl. H02m 5/12 US. Cl. 323-48 9 Claims ABSTRACT OF THE DISCLOSURE Transformer system including a large number, on the order of nine or more, of magnetically independent transformer elements which are preferably mounted on a common base structure. Primary windings of the elements are interconnected with each other andyvith a voltage source, preferably being connected in series with each being formed by a small number of turns of a conductor of relatively large cross-sectional areafThe secondary windings are interconnected with each other and to a load, either in series or in parallel or with a combination of both. A magnetic core of each element is of short length and low reluctance. The voltage source may include switch means for producing oscillations at a high frequency, preferably on the order of 100,000 Hz.

This invention relates to a transformer of a compound nature and more particularly to a transformer system which is highly efficient in regard to voltage characteristics, power strength and phase and frequency characteristics, and also in regard to transformation of continuous or direct current to alternating current of any frequency, or to direct current. The transformer of this invention is of minimum size and weight and is readily and economically manufacturable.

In general, the transformer of this invention comprises a plurality of transformer elements which are preferably fixedly supported on a base structure to form an integral assembly. Each transformer element comprises primary and secondary windings on a core. The secondary windings are connected to a load, with either a series connection or a parallel connection or a combination of the two. In accordance with this invention, the primary wind ings are connected in series to form a series circuit which is coupled to a voltage source, and each of the primary windings is formed by a small number of turns of a conductor of relatively large cross sectional area to present a small ohmic resistance as compared to the internal impedance of the voltage source.

This arrangement is highly advantageous because of the following physical phenomena:

During the passage of alternating or of any interrupted current through a primary winding inductively coupled to a secondary winding, there arises (a) the inductive production of electric current in the secondary winding and (b) an inductive resistance or reactance in the primary winding. These phenomena are immediately correlated. In particular, the greater the amount of current absorbed in the primary winding, the less the resistance or reactance developed in the winding, which is overcome by the alternating voltage of the source.

For these reasons, if from the secondary winding one takes all possible power which the primary winding can supply, the inductive reactance of the primary winding substantially disappears and if a conductor of large cross section is used in the primary winding, a very low ohmic resistance is presented. Therefore, with a transformer having a small number of turns in the primary winding and with a conductor of large cross sectional area, a very ice small resistance to the passage of current is obtained. With the arrangement of this invention, a plurality and preferably a very large number of transformer elements are provided with the primary windings thereof connected in series, without presenting a large resistance, and with a substantial reduction in the overall volume and weight, particularly in the weight of the required core structure. A further advantage is that the transformer can be operated at very low frequencies as compared to transformers of prior art constructions of the same size, and another advantage is obtained at high frequencies in that the hysterises losses are minimized because of the small volume of the required core material.

It is important to consider that since with the above described features, the remaining ohmic resistance in each primary coil or winding is small in relation to the internal impedance of the voltage supply, it does not add any substantial resistance to the passage of the feeding current, even when multiplied to a certain extent. Accordingly, if with the circuit of a primary winding of a transformer having a small ohmic resistance, another primary winding or another transformer of an equally small ohmic resistance is connected, the difference in current flow will be very small as compared to that obtained with a single transformer, providing the total of the resistances of the primary windings of the two transformers is a small part of the total resistance of the source. All the same time, the same power can be taken from the second transformer as is taken from the first, and the power output is substantially doubled, with a corresponding increase in efficiency.

This may be clarified by consideration of the following arithmetical example:

If a voltage source connected to the primary winding of a transformer has an internal resistance of ohms and the primary winding has a resistance of 2 ohms, a total resistance of 102 ohms is presented. If the primary winding of a second transformer is connected in series with the primary winding of the first, the total resistance of the two primary windings is 4 ohms and the total re sistance of the circuit is 104 ohms. Thus, with one transformer the total primary circuit resistance is /102 of the total resistance and with 2 transformers, the total resistance is of the total resistance. However, the percentage difference between 102 and 104 is very small with the result that the current flow is substantially the same and the transformers are excited substantially the same in both cases. However, with two transformers, generally twice as much total power is produced. With additional transformers, the total power can be progressively increased, although not in direct proportion.

The arrangement is particularly advantageous when each of the primary windings has a very small number of turns of a conductor of large cross sectional area.

The optimum number of elements required to form a compound transformer of this invention may be calculated from the following formula:

N V/RI where N=number of transformer elements,

V=supply voltage,

R=ohmic resistance of the primary winding of each element, and

I= current required to pass through each primary wind- In one preferred application, the transformer is operable as a simple low frequency transformer, for transforming 25, 50, 60 or 420 cycle current, for example.

In another preferred application, electronic switching means are provided for coupling the series-connected primary windings to a voltage source, so as to produce high frequency oscillations of current in the primary windings. For example, a frequency of 100,000 cycles per second may be used. With this arrangement, the cores of the transformer elements can be extremely small, while high efficiencies are obtained.

According to a further feature of the invention, rectifier means are provided for coupling the secondary windings of the transformers to a load, to produce a unidirectional current in the load. This feature is particularly advantageous when a high frequency current is applied to the primary windings.

Still another feature of the invention relates to the mounting of the transformer elements. The elements may be mounted by using bolts or the like to secure them to n kbase structure, or by using a potting compound or the This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction 'with the accompanying drawing which illustrates a preferred embodiment and in which:

FIGURE 1 is a schematic electrical diagram of a transformer system constructed in accordance with the principles of this invention; and

FIGURE 2 is a cross sectional view of a compound transformer of the system of FIGURE 1.

Reference numeral generally designates a transformer system constructed in accordance with the principles of this invention. In the system 10, nine transformer elements 11-19 are provided having primary windings 21-29 and secondary windings 31-39 on cores 41-49, as diagrammatically shown in FIGURE 1. The transformer elements 11-19 may be mounted on a common base structure to form a single integral compound transformer generally indicated by reference numeral 50, a preferred construction being described hereinafter in connection with FIGURE 2.

In accordance with this invention, the primary windings 21-29 are connected in series, to form a series circuit between lines 51 and 52. Lines 51 and 52 may be coupled either directly to a voltage source 54, or indirectly to the voltage source 54 through a high frequency switch unit 55, depending upon the position of ganged selector switch contacts 56-59. Thus, in the illustrated positions of the contacts 56-59, output terminals 61 and 62 of the voltage source 54 are connected directly through contacts 56 and 57 to the lines 51 and 52. In the other position of the contacts 56-59, terminals 61 and 62 of the voltage source 54 are connected to input terminals 63 and 64 of the switch unit 55, through the contacts 56 and 57, while output terminals 65 and 66 of the switch unit 55 are connected through the switch contacts 58 and 59 to the lines 51 and 52.

The secondary windings 31-39 may be connected in parallel, in series, or with a combination of both types of connections, as is illustrated. In this arrangement, the windings 31-33 are connected in series to form a first series circuit, the windings 34-36 are connected in series to form a second series circuit and the windings 37-39 are connected in series to form a third series circuit, the first, second and third series circuits being connected in parallel between circuit points 67 and 68. Circuit point 67 is selectively connected through a switch 69 either to one terminal of a load 70 or to an input terminal of a rectifier unit 71, connected to the load 70, the circuit point 68 being connected to the other terminal of the load 70. The rectifier unit 71 may comprise a series diode 74 and a parallel smoothing capacitor 73, in parallel with the load 7 0. Thus, either alternating current or direct current may be supplied to the load 70.

In accordance with this invention, each of the primary windings 21-29 is formed by a small number of turns of a conductor of relatively large cross sectional area to present a small ohmic resistance as compared .4 to the internal resistance or impedance of the voltage source 54. This arrangement is highly advantageous both at low frequencies, as when the conductors 51 and 52 are directly connected to the source 54 with the source 54 supplying a low frequency current such as 25, 50, 60 or 420 cycle current. At low frequencies, the compound transformer 50 may have a very small size and weight, while supplying power and high efficiency. At the same time, the system is highly effective at high frequencies, in that the cores 41-49 of the transformers may be of small size, to produce very low hysterises losses.

The high frequency switch unit 55 is preferably an electronic type such as one comprising a vibrator or oscillator and power amplifier stages, supplied with voltage from the source 54. Either vacuum tubes or transistors may be used. By way of example and not by way of limitation, the switch unit 55 may be operated at a frequency on the order of 100,000 cycles per second.

With regard to the cores 41-49, they are preferably of materials having minimum eddy current and hysterises losses, particularly at higher frequencies, when the unit 55 is used. By way of example, silicon iron alloys 0r ferrite materials may be used.

The rectifier 74 is preferably a solid state rectifier, of selenium copper hypoxide, silicon, germanium, or the like.

The transformer elements 11-19 are preferably secured to a common base structure as by securing them to a base with the use of bolts or the like. Preferably, the transformer elements 11-19 may be disposed within a common metallic housing 75, with an incapsulating material 76 or pottingcompound surounding the elements 11-19 and filling the housing 75, as shown in FIGURE 2. The switch unit 55 may be mounted on the outside of the housing 75.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

I claim as my invention:

1. In a transformer system, a plurality of transformer elements on the order of 9 or more each including a core and primary and secondary windings on said core, means interconnecting said primary windings to form a primary circuit, first coupling means for connecting said primary circuit to a voltage source, means interconnecting said secondary windings to form a secondary circuit, and second coupling means for coupling said secondary circuit to a load, said cores being magnetically independent and each of said cores being of magnetic material and forming a magnetic circuit of short length and low reluctance to couple said primary and secondary windings thereon, whereby the total size and weight of said plurality of transformer elements is substantially less than the size and weight of a single transformer operable with comparable efliciency between said voltage source and said load.

2. In a transformer system as defined in claim 1 for connection between a voltage source having a certain internal impedance and a load having a certain impedance, said primary winding being connected in series and each being formed by a small number of turns of a conductor of relatively large cross-sectional area to present a small ohmic resistance as compared to said internal impedance of said source.

3. In a transformer system as defined in claim 1, said second coupling means including means effectively coupling a plurality of said secondary windings in series relation.

4. In a transformer system as defined in claim 1, said second coupling means including means effectively coupling a plurality of said secondary windings in parallel relation.

5. In a transformer system as defined in claim 1, a base structure and means fixedly supporting all of said transformer elements on said base structure.

6. In a transformer system as defined in claim 1 for connection between a voltage source having a certain internal impedance and a load having a certain impedance, said primary windings being connected in series and each being formed by a small number of turns of a conductor of relatively large cross-sectional area to present a small ohmic resistance as compared to said internal impedance of said source, a base structure, means fixedly supporting all of said transformer elements on said base structure, and said second coupling means including means providing a combination of series and parallel connections between said secondary windings.

7. In a transformer system 'as defined in claim 1, said first coupling means comprising high frequency switch means for producing high frequency oscillations of current in said primary windings.

8. In a transformer system as defined in claim 7, a frequency of said oscillations being on the order of 100,- 000 Hertz.

9. In a method of making a transformer system for supplying current to a load having a certain impedance from a voltage source having a certain internal impedance, the steps of providing a plurality of cores of magnetic material to form independent magnetic circuits each having a short length and a low reluctance, providing primary windings on said cores each having a small numnecting said primary windings in series to form a primary circuit, providing means for coupling said primary circuit to said voltage source, providing a secondary winding on each of said cores, and providing coupling means for coupling said secondary windings to said load.

References Cited UNITED STATES PATENTS 3/1957 Bichel 323- X 2/1958 Jones 336- OTHER REFERENCES Practical Design Problems in Transistor D.C./D.C.

*Convertors and D.C./A.C. Inverters by Towers; IEEE Paper No. 2984B, April 1960, p. 1378.

JOHN F. COUCH, Primary Examiner G. GOLDBERG Assistant Examiner US. Cl. X.R. 

